The Science of Sleep

(gentle music) Today we're going to explore circadian rhythms, the natural process our brains use to regulate our sleep-wake cycle throughout the day. This biological process is constantly moving to and fro. It's a great reminder of an idea so important to mindfulness: impermanence. That is, that everything is changing in our minds, our bodies, and the world around us. The word circadian comes from two Latin words. Circa, which means about and diem, which means day. Animals and plants have naturally occurring rhythms that recur every 24 hours, some of which are influenced by light and dark, but let's focus on us humans. Our eyes have adapted to using light. Bight light and dim light, multicolored light and monochromatic light. Our eyes are connected via the optic nerve to the back of the brain. Here, a tiny region is responsible for controlling the circadian rhythms. It's essentially a master clock, which, based on the light signals it receives, regulates the production of a variety of hormones, affecting sleep, body temperature, and other key bodily functions. Say what going out camping, a weekend journey with just natural light, for our brain to experience. During the day, the sun's light is taken in through the retina and a signal tells our brains, specifically the pineal gland, not to produce melatonin, the hormone that makes us sleepy. But when the sun sets, there's nothing at the distant twinkling star light to hit our eyes. Now the opposite signal is sent. Begin the melatonin production. And as a result, we start to get drowsy. In the darkness, we soon fall asleep. When the sun starts to rise bright and early, a light hitting the eyelids illuminates the back of the eye, which sends a message to the brain's clock, saying we need a halt in the melatonin production and the pineal gland makes no more. As the effect of melatonin starts to wane, we wake up ready to start our day. With light pouring into our eyeballs, we stay wide awake, ready to enjoy another great day of activity. As you go about your day, take comfort in the biological cycles in continuous motion, which, just like life, are changing from one moment to the next....